As a number-of-scanning-line conversion apparatus for converting, for example, 525 scanning lines per frame of video signal on NTSC system or 625 scanning lines per frame of video signal on PAL system to 1050 or more scanning lines, such apparatus that classifies an input picture depending on its pattern and processes every pattern so as to make the picture have higher definition was proposed in the past (Japanese Laid-Open Patent Application No. H7-75066).
By employing such number-of-scanning-line conversion apparatus, it is possible to improve remarkably the quality of, for example, natural picture taken by camera. In such apparatus, however, in order to improve the picture quality particularly in a vertical direction, a process for emphasizing a high-frequency component in the vertical direction is provided. In that case, there may be no problem with the above-described natural picture, whereas with an artificial picture such as a telop superimposed on the natural picture, a bad effect will be caused that part of picture has an excessive high intensity and so on.
Specifically, in the telop superimposed on a natural picture for example, the frequency in a vertical direction is extremely high at its edge portion. Thus, if the high-frequency component in the vertical direction is emphasized in such picture, an intensity level at the edge portion will be too high and become liable to be noticed. For this reason, deterioration of picture quality such as so-called line flicker and defocus due to characteristics of a cathode-ray tube for displaying the picture will arise.
In addition, such picture-quality deterioration will also be caused, in the other case than the above-described telop, for example, when the menu for adjusting a television set is superimposed on a natural picture for display. Moreover, the emphasis on high-frequency component in the vertical direction of picture is not limited to the video-signal processing which performs the number-of-scanning-line conversion with high accuracy as described above, and is also applied to the number-of-scanning-line conversion by so-called vertical interpolation or general vertical enhancement. In these cases, the picture-quality deterioration described above will be caused likewise.
In order to solve this problem, the applicants of the present invention proposed previously a video-signal processing apparatus in which an image-processed signal and an original signal are compared with a reference level, and these signals are switched over to be taken out depending on the comparison result (Japanese Laid-Open Patent Application No. H11-355613).
Specifically, as is shown in FIG. 1, a video signal input to an input terminal 1 is supplied to a number-of-scanning-line converter and picture-quality enhancer circuit 2 which performs a double-speed conversion of converting twice the number of scanning lines and also processing to enhance the picture quality depending on the picture at that time. An output of the number-of-scanning-line converter and picture-quality enhancer circuit 2 is supplied to an adaptive suppressing unit 3 against emphasized component, which suppresses a portion of a video component in the vertical direction overemphasized and provides an output video signal.
The adaptive suppressing unit 3 against emphasized component is provided with a delay circuit 4 for delaying the video signal input in the input terminal 1 by a time required for signal processing in the number-of-scanning-line converter and picture-quality enhancer circuit 2. An output of the delay circuit 4 and an output of the number-of-scanning-line converter and picture-quality enhancer circuit 2 are supplied to an emphasized-component detector circuit 5, which compares differences between the respective outputs and a reference signal level obtained at a reference-signal input terminal 6 with each other and detects an overemphasized component. When the emphasized-component detector circuit 5 detects the overemphasized component, the relevant portion of video signal is supplied to an adaptive emphasized-component suppressor circuit 7 which performs suppressive processing to output the processed signal.
FIG. 2 is a diagram showing an example of more specific structure of processor circuits shown in FIG. 1. In this example, a video signal obtained at an input terminal 11 is supplied to a double-speed processor circuit 12 which performs the so-called double-speed conversion processing to convert twice the number of scanning lines. When the double-speed processor circuit 12 performs the double-speed conversion processing, it also performs the picture-quality enhancement processing. In this example, two scanning-line signals (the two signals are termed ha and hb) converted from one scanning-line signal by the double-speed conversion circuit 12 are output in parallel at the same time. The two scanning-line signals ha and hb are supplied to separate adaptive emphasized-component suppressor circuits 13a and 13b, respectively. Each of the adaptive emphasized-component suppressor circuits 13a and 13b performs suppressive processing on the emphasized component based on the respective outputs of separate emphasized-component detector circuits 16a and 16b. The adaptive emphasized-component suppressor circuit is also termed a peak limiter. Each output of the adaptive emphasized-component suppressor circuits 13a and 13b is supplied to a time-axis converter circuit 14 which converts the time axis for outputting each scanning-line signal and outputs the resulting signal as a video signal on one system.
Each of the emphasized-component detector circuits 16a and 16b receives each of the two scanning-line signals ha and hb output by the double-speed processor circuit 12, and also each of signals delayed by a time required for signal processing in the double-speed processor circuit 12. They further receive the reference level signal obtained at the reference-signal input terminal 17 respectively, and thus detect the overemphasized component in the vertical direction.
Each processing of detecting the emphasized component by the emphasized-component detector circuits 16a and 16b is performed as follows. For example, where a reference level is set by the reference signal obtained at the input terminal 17, a signal supplied from the delay circuit 15 being referred to as an input signal, and outputs of the double-speed processor circuit 12 being referred to as a converted signal, three differential signals of a. (input signal—reference level), b. (converted signal—reference level), c. (input signal—converted signal) will be obtained. A specific example using these three differential signals a, b, and c will be described below. When (differential signal a<0) and (differential signal b>0), the adaptive emphasized-component suppressor circuit 13a or 13b processes to suppress the number-of-scanning-line converted signal down to the reference level. When (differential signal a<0) and (differential signal b<0) the adaptive emphasized-component suppressor circuit 13a or 13b outputs the number-of-scanning-line converted signal as it is.
The reference-signal level is selected to characteristics of a display means (cathode-ray tube, etc.) which receives an output of this processor circuit. By selecting an appropriate reference level, it is possible to suppress the peak of overemphasized video signal down to an appropriate level and utilize such emphasized-component that contributes to the picture-quality enhancement as it is.
However, in this kind of conventional emphasized-component suppression processing, the original signal and the converted signal compared with each other in the emphasized-component detector circuit (corresponding to emphasized-component detector circuits 16a and 16b in FIG. 2) are such that always reside in a fixed relation. Because of this fact, exact detection of emphasized component cannot be made, so that a properly emphasized component may be suppressed by mistake, or inversely the overemphasized component may not be suppressed, which will lead to picture-quality deterioration.
Moreover, when a phase of scanning lines created by the scanning-line conversion differs from a phase of input signal, only by comparing with the input signal delayed by the same time as that required for the number-of-scanning-line conversion process, the exact detection of emphasized component cannot be performed. This also poses the same problem that the duly emphasized component is suppressed erroneously or the overemphasized component cannot be suppressed.
The present invention has been made in view of the foregoing points and aims to enable satisfactory suppression of the overemphasized component when converting the number of scanning lines of video signal.